CORRELATION OF CERIUM ANOMALIES WITH INDICATORS OF PALEOENVIRONMENT

Among 21 whole-rock samples of the Upper Cretaceous Niobrara Formation from Colorado, the abundance of cerium relative to other rare earth e lements (Ce anomaly), the weight percent organic carbon (%C-org), and the intensity of bioturbation all covary. This covariation is provocat ive because %C-org and intensity of bioturbation track changes in the concentration of oxygen in the local water column at the time of depos ition (Savrda and Bottjer 1989). Ce anomalies in apatite-rich fraction s of the Maastrichtian Zumaya-Algorta Formation from France and Spain and the Miocene Monterey Formation from California show changes that a lso may coincide with changes in ancient oxygen levels, Our results fo r the Niobrara samples are the closest correspondence demonstrated bet ween paleo-redox conditions and Ce anomalies, but we cannot yet determ ine whether the correspondence reflects a cause-and effect relationshi p, Variation in Ce anomalies is influenced by a number of factors, inc luding terrigenous input, depositional environment, and diagenetic con ditions. Potential interplay of these factors prevents a unique interp retation of our whole-rock data; dissecting whole-rock Ce anomalies th rough analysis of isolated sedimentary components, though, is a promis ing avenue of research.